1. Field of the Invention
The present invention relates to an emergency locking device for an extractable strap in a vehicle safety belt comprising a pivoted locking means adapted to be moved from an idle position to a locking position in which the locking means forces the strap against a rear surface, so that the strap is locked between the rear surface and the locking means. The emergency locking device is primarily intended for use in safety belts in motor cars.
2. Discussion of the Prior Art
Vehicle safety belts with automatically retractable straps are previously known. In a safety belt of this type, the strap is wound onto a rotatably mounted shaft. The shaft is operated by a spring which is stressed when the strap is extracted, and thus can retract the strap, so that the strap is rewound onto the shaft, when the belt is not in use. A safety belt of this type is provided with a vehicle or strap sensitive means for locking the shaft, when the vehicle is being braked or turned heavily, so that the strap cannot be further withdrawn from the shaft. In this way, the person in the safety belt will be reliably restrained. However, also when the safety belt is used, normally a number of strap turns remain on the shaft. This fact entails the disadvantage that due to the so called film-roll-effect, i.e. a compression of the strap turns on the shaft, a further portion of the strap can be withdrawn from the shaft, in spite of the fact that the strap shaft is locked, when the vehicle is heavily decelerated, for example in a collision, and the person restrained in the seat belts is thrown forwardly. The portion of the strap further withdrawn can have a length of 10-15 centimeters and causes a large risk for the person restrained in the seat belt to hit a portion of the vehicle, for example the steering wheel or the windscreen.
It is previously known to provide safety belts with particular strap locking means to avoid the above mentioned disadvantage. Strap locking means of this type may comprise a turnable locking means which can be moved from an idle position to a locking position in which the locking means forces the strap against a rear surface, so that the strap is clamped between the rear surface and the locking means. The strap is caused to run either in a loop between locking rollers which can be moved to locking positions by the strap, or over a turnable locking means which can be swung into a locking position by the strap, when the strap is subject to a heavy load. A device of the last mentioned type is shown and disclosed in DE Offenlegungsschrift No. 2 420 848. These two types of prior art devices have both the disadvantage that the strap has to run over further surfaces which increase the friction when the strap is withdrawn and thus require a more powerful spring for the retraction of the strap. An increased spring force makes the safety belt more difficult to fasten and more unpleasant to wear, because the safety belt exerts a heavier pressure on the chest of the person restrained by the belt.